1. Field of the Invention
The invention relates to a power supply, including a controller and a power element, wherein a DC compensation voltage is present at a first output of the power element, to which a load having a variable current draw can be connected.
2. Description of the Related Art
The situation frequently arises, particularly in industrial systems, whereby a load is supplied by a power supply and in the process draws power that is not predetermined. A mains power supply network, to which the power supply is connected, generally is not fully protected against failure. Different measures are therefore known in order, in the event of mains failure, to ensure further supply of the load for a certain period of time. This is above all the case in safety-relevant applications. One example includes cable cars and chairlifts, which according to various regulations require a battery back-up, in order to maintain a control voltage (in most instances 24V) for the emergency supply of signals as well as control and communications facilities.
Rechargeable back-up batteries used in such systems should achieve as long a service life as possible to keep the maintenance outlay of a system low. With such rechargeable batteries, attention is therefore paid if necessary to a gentle charging and discharging process and to a protection against rechargeable battery deep discharge.
This is taken into account for instance with the use of an uninterruptable power supply system (UPS system) for a DC voltage, where a rechargeable back-up battery is operated by a charge controller and switched off in the event of deep discharge. With such systems, the load is in most instances supplied with the nominal output voltage of the power supply. Only in an emergency situation will the load be switched to the, in most instances, higher voltage of the charged rechargeable battery.
A UPS system represents a comprehensive solution, because the rechargeable battery can be charged with an attuned and optimized charging current characteristic by the charge controller, without the load being influenced. At the same time, this method is very complicated, since a dedicated UPS assembly is in most cases required in addition to the power supply.
Solutions without a dedicated UPS assembly are therefore also known. In such solutions, the power supply is selected such that there is the possibility to limit the output current to a defined value above the nominal current. A rechargeable back-up battery is directly connected to the output of such a power supply by way of a fuse or a cut-out, i.e., in parallel to the connected load. In the event of a mains outage, the rechargeable battery directly takes over the supply of the load.
The output voltage of the power supply is set such that it corresponds to the end-of-charge voltage of the rechargeable battery. Provided the rechargeable battery is not completely charged, the power supply is operated at its power limit. The difference between the consumption of the load and the power limit is routed into the rechargeable battery as a charging current. A controlled charge is not possible here. The load is operated with the end-of-charge voltage after charging the rechargeable battery. This is nevertheless generally unproblematic on account of an adequate tolerance of the supply voltage range of the load (at least at 24V consumers).
Aside from the uncontrollable charging current already mentioned, there is a further disadvantage in that, with an intentional deactivation of the system, the rechargeable battery also always has to be separately disconnected. Otherwise, there is the risk of a deep discharge involving damage to the rechargeable battery resulting therefrom.